Washington insists the detained American has diplomatic immunity and killed the Pakistanis in self-defense as they tried to rob him at gunpoint. It says the man's detention is illegal under international agreements covering diplomatic ties.
Pakistani leaders, facing a groundswell of popular anger triggered by the incident, have avoided definitive statements on the status of the American, whom they have named as Raymond Davis. Davis's next court appearance is set for Feb. 11.
Two senior U.S. officials told The Associated Press on Monday that talks involving Afghanistan, Pakistan and the U.S. set for Feb. 24 in Washington are now in doubt because of the spat. The officials spoke on condition of anonymity because they are not authorized to release the information publicly.
The talks are supposed to be held at the ministerial level, meaning U.S. Secretary of State Hillary Rodham Clinton and Pakistani Foreign Secretary Shah Mahmood Qureshi would participate. It's possible that they could simply be downgraded to included just lower-level officials.
Pakistani Foreign Ministry spokesman Abdul Basit said the two countries must not lose sight of the strategic imperatives of their relationship.
"Our relations are mature enough to navigate through difficulties," he wrote in a text message.
U.S. Ambassador to Pakistan Cameron Munter met with Pakistani President Asif Ali Zardari on Monday and pressed him to release Davis. That meeting and recent U.S. press statements have indicated growing frustration with an ally considered key to ending the conflict in Afghanistan.
Pakistan risks looking like an American lackey if it caves into demands to free Davis. But it's also a risk to ignore the U.S., which provides it with billions of dollars in military and other aid.
Federal officials say Davis' fate is up to courts in Punjab province, while provincial officials say the federal government must inform them whether Davis has immunity and has not done so. The two governments are controlled by rival political parties, which further complicates the matter.
Davis shot the two men Jan. 27 in the eastern city of Lahore. A third Pakistani, a bystander, died when a car rushing to back Davis up struck him. Police have said they want to question the Americans suspected in that death as well.
Clinton spoke with Zardari by phone last week about the diplomat's case and also raised it with Pakistan army chief Gen. Ashfaq Parvez Kayani on the sidelines of an international security conference in Germany at the weekend, State Department spokesman P.J. Crowley said.
"We continue to make it clear to the government of Pakistan that our diplomat has diplomatic immunity and in our view was acting in self-defense and should be released," Crowley said Monday.
The wife of one of the men who Davis shot committed suicide on Sunday, explaining beforehand that she feared her husband's killer would be freed without trial. Her death further inflamed anti-American sentiment.
In Pakistan's northwest Tuesday, troops backed by airstrikes killed at least 12 suspected militants. The clash occurred in the tribal region of Orakzai, where the military has been waging an offensive against the Taliban, said Aurangzeb Khan, a local government official.
In the Bannu area, near the tribal belt, a roadside bomb targeting an army convoy killed two soldiers, including a captain, and wounded four others, a police official and an intelligence official said. They spoke on condition of anonymity because the incident involved the army.
Near the northwest city of Peshawar, a pair of bombs struck an abandoned security checkpoint and a convoy of police responding to the scene, local police official Amir Sultan Khan said. An officer died, while four others were wounded.
Also in the Peshawar area, a tanker believed to be carrying fuel for NATO forces across the border in Afghanistan caught on fire while stuck in a traffic jam, police said. The fire quickly spread to other tankers and vehicles nearby, releasing huge black plumes of smoke.
There was no immediate report of casualties and it was unclear whether the blaze was sparked accidentally or the result of an attack, police official Mir Afzal Khan said. Militants and criminals in Pakistan frequently attack trucks carrying supplies for U.S. and NATO forces across the border.
Associated Press writers Anne Gearan in Washington, Riaz Khan and Rasool Dawar in Peshawar, Mohammad Ejaz in Bannu and Hussain Afzal in Parachinar contributed to this report.